BMW would consider the 10w30 too light for current ambient temperatures.
20W-50 was among the oil grades actually recommended for this car when it was new.
I put the 10w30 in it last fall, and wanted to at least get 3K out of it before draining it.
My original plan was to begin using the car again in April.
I did not anticipate that we would have as cold and as wet a spring as we did, and as a result, I've only put the car back on the road this week.
A convertible summer car has no special value when it's cold and wet.
We actually saw 10"+ of rain in April here, which is about 25% of the average yearly pricipitation for this region.
Anyway, you are probably right, and the engine probably doesn't need a fifty, unless I find an autobahn around here to run flat out for an hour or so.
Nonetheless, a fifty falls within BMW's American recommendations for this engine, so it wouldn't do any harm.
And it is so gosh-darn cheap, for Eneos.